The Treatment Section continues to investigate predictors that might be useful for patient-treatment matching to improve the delivery of appropriate treatments to individual patients. In a recently completed project, we conducted a retrospective analysis of data from two randomized clinical trials to test the hypothesis that pre-treatment benzodiazepine use as reported on the Addiction Severity Index (ASI), a widely used clinical interview, would predict treatment outcome. Upon enrollment in methadone maintenance therapy, 361 cocaine/opiate users were randomly assigned to 12-week voucher- or prize-based contingency management or control interventions. The relationship between pre-treatment illicit benzodiazepine use (days of use in the last 30) assessed on ASI prior to initiating treatment and outcome on a range of outcome measures was analyzed. Outcome measures were: urine drug screens; quality of life and self-reported HIV-risk behaviors; and current DSM-IV diagnosis of cocaine and heroin dependence at the end of treatment. In the group receiving contingency management, participants who had reported one or more days of benzodiazepine use pre-treatment had significantly worse outcomes on in-treatment cocaine use, quality-of-life scores, needle-sharing behaviors, and current heroin dependence diagnoses at study exit compared to those who reported no use. In the control group, benzodiazepine users had significantly higher in-treatment cocaine use but did not differ from non-users on psychosocial measures. Thus, in a sample of non-dependent benzodiazepine users, self-reported illicit benzodiazepine use on the ASI, even at low levels, predicted worse outcome on cocaine use and blunted response to contingency management. These findings suggest that benzodiazepine users, even those with relatively modest benzodiazepine use, represent high-need, treatment-resistant patients. Benzodiazepine users in methadone maintenance may benefit from more intensive psychosocial interventions as alternatives, supplements, or prerequisites to contingency management targeted at other drug use. Such interventions could include individualized case management and need-service matching. The utility of these findings is increased by the fact that they were based on self-reported benzodiazepine use collected using the ASI, an assessment tool widely used in both community and research treatment programs.